Nkurunziza, who ruled the country for almost 15 years, died at the aged 55 of what the government said was “heart failure”.
But speculation is rife he may have caught the coronavirus, as his wife was flown to Nairobi for treatment for the virus just two weeks before his death.
Nkurunziza died shortly after an election won by his handpicked successor Evariste Ndayishimiye, who was sworn in last week.
Friday was declared a national holiday for the funeral. School children in uniform and citizens lined the roads waiting for the funeral convoy to pass.
The stadium in Gitega where the funeral ceremony is to be held was packed with citizens from across the country, all dressed in white at the request of authorities.
Nkurunziza will be buried at a monument recently built in Gitega at the site of another structure which was to be dedicated to victims of the country’s various crises over the years, but was never inaugurated.
Nkurunziza, a devout evangelical who believed he was chosen by God to lead Burundi, left behind a deeply isolated country in political and economic turmoil.
His 2015 run for a third term in office sparked protests and a failed coup, with violence leaving at least 1,200 dead while some 400,000 fled the country.
Burundi was plunged into a political crisis in 2015 when Nkurunziza sought a controversial third term in office.